This invention relates to a method of making aluminum-zirconium antiperspirants of enhanced efficacy in polyhydric alcohols and to the products obtained.
Aluminum halide antiperspirant compounds are well known. The addition of zirconium compounds to aluminum complexes generally enhances the efficacy of the antiperspirants because of the depolymerization of aluminum species in the presence of zirconium. As the concentration of zirconium increases, more monomeric and polymeric aluminum cations are formed, and a change in the structure of the polymers is also observed. This accounts for improvements in aluminum-zirconium antiperspirants over the use of aluminum antiperspirants alone.
Alcohol-soluble aluminum complexes are disclosed in U.S. Pat. No. 3,507,896 to Jones et al, and can be made by reacting aluminum metal with aluminum chloride or hydrochloric acid at 75-110xc2x0 C. in the presence of a polyhydric alcohol and water. There are no restrictions on the amount of water that can be used.
Current processes for making aluminum-zirconium (hereinafter Al and Zr) antiperspirants involves making Al and Zr salts in aqueous solutions separately, combining the solutions, adding polyhydric alcohols either before or after combining the solutions and evaporating excess water. Such methods require the evaporation of large amounts of water from the dilute solutions and thus is not economical. In order to make activated Alxe2x80x94Zr antiperspirants, the combined solution is held at elevated temperatures for lengthy periods. Such heating in aqueous solution forms high molecular weight polymers of Zr species. The presence of such polymers reduces the effectiveness of antiperspirant compositions.
The Al species in aluminum or aluminum-zirconium antiperspirants are generally of three types; a) fast reacting Al3+ ion which consists of monomers, designated as Ala; b) slower reacting polyhydrolysis species, designated as Alb; and c) very slow reacting high molecular weight polymers and amorphous solids, designated as Alc.
AlCl3.6H2O consists of 96% monomeric Ala species, whereas 50% by weight aluminum chlorhydroxy solutions contain over 95% of high molecular weight Alc polymeric species.
The prior art teaches several methods of determining the degree of polymerization of Al complexes.
One of these is known as high performance liquid chromatography (HPLC). The highest molecular weight Al species are eluted first, known as Band I. Bands II and III designate intermediate molecular weight Al complexes. Band IV designates the lowest molecular weight Al complexes, including monomers and probably dimers. Band V designates small molecules that do not include Al. The relative area of one or more peaks is determined in order to characterize the distribution of polymeric species in the Al complexes formed.
The relative peak areas or peak regions, as a percentage of total peak area, is obtained by dividing the integral curve area of a particular peak or region by the sum of the integral curve areas of all of the resonance peaks. Desirable Alxe2x80x94Zr antiperspirant compositions exhibit more than 60% of aluminum species of Bands III and IV, and 0% to 5% of Band I.
Another method of determining the degree of aluminum complex polymerization includes Ferron Analysis, which reacts the Al complexes with a ferron reagent, and characterizes the complexes on the basis of three species types; as low molecular weight Al3+ monomers, hereinafter Ala; as intermediate molecular weight complexes from the dimer up to about Al13, hereinafter Alb, and as high molecular weight aluminum hydroxide complexes, hereinafter Alc, which takes the longest time to react with the ferron reagent. It is an objective of the present invention to provide an aluminum-zirconium antiperspirant of enhanced efficacy with an increased amount of depolymerized aluminum species, i.e., wherein at least 25%, and preferably more than 40%, of the aluminum species are monomeric.
Still another method used is 27Al nuclear magnetic resonance (NMR) to determine the structure of aluminum in the Alxe2x80x94Zr antiperspirant. For the present application, data were collected from about +160 to xe2x88x92160 ppm.
Most of the known methods of preparing antiperspirants of enhanced efficacy involve heating diluted basic aluminum chlorhydroxide solutions. The HPLC chromatogram of the salt has a peak area ratio of Band III to Band II of at least 0.5. However, the solution is unstable, and over time the Band III to Band II area is lowered to 0.3 or less. However, Band IV, which includes Al3+ monomers, is not mentioned in the prior art. A higher Band IV will increase the effectiveness of the antiperspirant.
A method of producing the present Alxe2x80x94Zr complexes from an aluminum halide and zirconium oxyhalide, together with a polyhydric alcohol, that has a Band III plus Band IV of at least 60%, and preferably of about 80 to 90%, would increase efficacy as an antiperspirant and thus would be highly desirable. It is also desirable to obtain a stable solution of an Alxe2x80x94Zr composition in a concentration of 20-45% by weight.
The present method comprises forming a reaction mixture of an aqueous solution of a soluble aluminum salt, a zirconium compound, an amino acid buffer, a polyhydric alcohol having at least two carbon atoms to which at least two hydroxyl groups are attached and mixtures thereof, and aluminum metal, maintaining the reaction mixture at a temperature of about 100-140xc2x0 C. to provide an Alxe2x80x94Zr complex in the polyhydric alcohol at a concentration of about 20-45% by weight on an anhydrous solid basis. The product obtained is characterized by a high Band III and Band IV content, having a HPLC relative area of at least 60%, and 0% to 5% of the total chromatogram peak area eluting at the shorter retention times of Band I. This composition contains monomeric Ala species of at least 25%, and preferably of above 40%, and is stable in solution at concentrations of at least 20%, and preferably 30-35% by weight.